Optical fiber fixing member, method of manufacturing the optical fiber fixing member, optical fiber array, and method of manufacturing the optical fiber array

ABSTRACT

An optical fiber fixing member having optical fiber engagement grooves  2  and peaks  5  between the engagement grooves  2  is configured as a unitary structure by molding. A preform G is pressed with a mold  21  such that the concavities  25  of the mold  21 , which comprises convexities  26  and concavities  25  for the transfer of the engagement grooves  2  and the peaks  5 , respectively, are filled with the preform G only partially. The shape of the convexities  26  of the mold  21  is transferred, yielding optical fiber engagement grooves  2  whose surfaces are mold transfer surfaces  6 . Because the preform G fills the concavities  25  only partially, the peaks  5  between the optical fiber engagement grooves formed by the filling of the concavities  25  are free rounded surfaces  7  whose shape does not reflect the shape of the concave bottom portions  25   a  of the mold  21.

TECHNICAL FIELD

The present invention relates to an optical fiber fixing member forpositioning and fixing the ends of an optical fiber, a method formanufacturing this optical fiber fixing member, an optical fiber array,and a method for manufacturing this optical fiber array, particularly byforming a unitary structure through molding.

BACKGROUND ART

In optical communications, light measurements, and other fields, membersfor positioning and fixing the ends of optical fibers are needed to formoptical connections among a plurality of optical fibers or between aplurality of optical fibers and other elements (for example, opticalwaveguides for the branching of optical communications signals). Methodsfor manufacturing such optical fiber fixing members by press moldingwith good productivity and reproducibility have been used in recentyears.

For example, Japanese Unexamined Patent Application HEI8-292332(hereinafter abbreviated as “the Application”) describes a method inwhich a press mold for the transfer of grooves designed to fix the endsof optical fibers is manufactured by grinding, and glass is press-moldedwith the aid of this mold, yielding an optical fiber fixing member.According to the Application, the resulting optical fiber fixing memberis advantageous in that peak chipping and damage to the optical fibersto be fixed can be prevented because the fixing member can be roundedoff such that the peaks between the fixing grooves have a specificradius of curvature in cross section.

The mold for the press molding of optical fiber fixing members describedin the Application is fabricated by grinding, and the ground surfaces ofthis mold inevitably contain numerous minute irregularities. Peaksbetween the V grooves for engaging and laying out optical fibers aretransfer-formed by the bottom portions of concavities in the mold, andbecause the transfer surfaces of the bottom portions of the concavitiesin the mold are formed as described above, irregularities due to surfaceroughness result, as do irregularities in the form of clearly visiblefolds.

With press molding, microscopic shapes are transferred in addition tothe macroscopic shape of the mold. In particular, the aforementionedmicroscopic shapes are transferred with high accuracy in moldingoperations in which the shape of the mold is transferred with very highaccuracy, such as near the optical fiber supports of optical fiberfixing members. Release films are sometimes formed on the transfersurfaces of molds, but the minute irregularities on the mold surfacesare transferred by the molds even in the presence of such release films.

Molded surfaces of optical fiber fixing members are therefore almostidentical in texture (surface hardness, fold-like irregularitiesresulting from machining, surface warping, and the like) to the surfacesof molds, and minute irregularities are also formed on the surfaces ofpeaks between the V grooves of a molded article.

When optical fibers are assembled into an optical fiber array by beingaligned in the V grooves and fixed in place by mechanical means or byadhesion, the optical fibers are aligned in the V grooves by beingpressed against the walls of the V grooves, but when minuteirregularities such as those described above are present on the peaksbetween the V grooves (with which the optical fibers are most likely tocome into contact, particularly during pressing), the lateral surfacesof the optical fibers are damaged, and microcracks form.

In view of this, the invention described in the Application entailsrounding off the peaks of optical fiber fixing members in cross section,and is thus useful in preventing optical fibers from undergoingcomparatively extensive chipping, notching, or the like. It isunavoidable, however, that numerous minute irregularities still remain,making it impossible to prevent microcracks such as those describedabove from forming. It is also indicated in the Application that thepeaks are rounded off by polishing, but such polishing involves cornerchamfering and is incapable of removing the numerous minuteirregularities on the peak surfaces.

A resulting drawback is that when light is transmitted by such anoptical fiber array, the propagating light is scattered at locationswhere microcracks are present, resulting in increased transmission loss.In addition, even cracks that are small enough not to have a directeffect on reduced transmission loss eventually develop into largercracks as a result of thermal stress due to variations in ambienttemperature, bringing about an increase in transmission loss. At theworst, optical fibers break and completely lose their ability tofunction as a light-transmitting medium.

Another drawback is that because a molded article and a mold adhere toeach other in the vicinity of optical fiber engagement portions duringthe formation of fixing grooves, the molded article exhibits poorrelease properties when it is removed from the mold following pressmolding, and a high fill factor is achieved by the molding material(material being molded) in relation to the volume of the mold cavity,making it more likely that molding burrs will form.

In addition, conventional optical fiber fixing members are molded bycompletely covering the molding surfaces of the mold with a moldingmaterial during the molding of the peaks between the optical fiberengagement grooves, so these peaks are mold transfer surfaces. Suchoptical fiber fixing members develop compression strain (stress) duringthe molding of the entire molding area of the optical fiber engagementgrooves. A resulting disadvantage is that cracks form near the opticalfiber engagement grooves, particularly in the bottom portions of theoptical fiber engagement grooves, where stress is apt to concentrate forstructural reasons.

An object of the present invention is to overcome the above-describeddrawbacks of prior art and to provide an optical fiber fixing memberwhose purpose is to ensure better release properties, to improve burrcontrol properties, and to prevent transmission loss from beingincreased by the microcracking of the optical fiber, as well as toprovide a method for manufacturing this member, an optical fiber arrayconstructed using the aforementioned optical fiber fixing member, and amethod for manufacturing this array.

DISCLOSURE OF THE INVENTION

The optical fiber fixing member of the first invention is an opticalfiber fixing member having a plurality of optical fiber engagementgrooves for positioning and fixing optical fibers, wherein at leastparts of the peaks between the optical fiber engagement grooves are freesurfaces. The term “free surface” refers to a surface of a moldedarticle that has been molded without any contact with the moldingsurface of the mold during molding and without the transfer of themolding surface of the mold. In addition, the term “optical fiberengagement groove” refers to a comparatively deep valley and includescases in which these valleys rise above the surface of the optical fiberfixing member because the peaks between the valleys are formed asconvexities on the surface of the optical fiber fixing member, and casesin which the valleys lie below the surface of the optical fiber fixingmember because the peaks are formed low above the surface of the opticalfiber fixing member.

The free surfaces between optical fiber engagement grooves may beseparated by at least one mold transfer surface (surface of a moldedarticle obtained by the transfer of the molding surface of a mold)extending in the drawing direction of the optical fiber engagementgrooves. This, for example, refers to cases in which optical fiberengagement grooves 2 (mold transfer surfaces) devoid of overlyingoptical fibers F are disposed between the optical fibers F (as shown inFIG. 1), and includes configurations (mold transfer surface/freesurface/mold transfer surface) in which free surfaces are furtherinterposed between the optical fiber engagement grooves 2 (mold transfersurfaces) devoid of overlying optical fibers F.

The optical fiber fixing member of the second invention is an opticalfiber fixing member having a plurality of optical fiber engagementgrooves for positioning and fixing optical fibers, wherein the surfacesof the optical fiber engagement grooves are formed by the mold transfersurfaces of a mold; and at least some of the surfaces of the peaksbetween the optical fiber engagement grooves are formed by free surfacesnot in contact with the mold.

Forming the peak surfaces between the optical fiber engagement groovesfrom free surfaces not in contact with the mold prevents the unavoidableminute irregularities formed in the mold as a result of a manufacturingprocess involving grinding from being transferred to the peak surfaces.There is, therefore, no damage to optical fibers from the minuteirregularities, and microcracking can be prevented.

In the invention described above, peaks formed from free surfaces shouldpreferably be as described in any of (i) to (iv) below.

(i) The free surfaces extend all the way in the longitudinal directionof the peaks.

(ii) The portions of the peaks on the side of the end face locatedcloser to optical connections are free surfaces (excluding case (i)).

(iii) The portions of the peaks on the side of the end face opposite theend face located closer to optical connections are free surfaces(excluding case (i)).

(iv) The portions of the peaks on the side of the end face locatedcloser to optical connections and on the side of the end face oppositethe end face located closer to the optical connections are free surfaces(excluding case (i)).

As used herein, the term “end face located closer to opticalconnections” refers to the end face of an optical fiber fixing memberwhose position corresponds to the position of the reception/transmissionend faces of optical fibers when these optical fibers are laid out andfixed in optical fiber engagement grooves, yielding an optical fiberarray.

Another feature of cases (ii) to (iv) is that when edges are formed asfree surfaces, the resulting peaks are also free surfaces in areas otherthan those occupied by elements regarded as edges. These edges resultfrom the intersection of surfaces that form optical fiber engagementgrooves and an end face that is located closer to optical connections,or an end face opposite the end face located closer to the opticalconnections. This will be described using FIG. 2. The portions of peaksbetween the optical fiber engagement grooves 2 near the edges a and b ofan optical fiber fixing member 1 are free surfaces when the edges, whichare located at both ends of the optical fiber engagement grooves 2, arefree surfaces. For optical fiber fixing members 1 in which at least oneof the edges a and b is a free surface, optical fiber fixing members 1in which free surfaces are limited to the portions of peaks 5 locatednear the free-surface edges lie outside the scope of the presentinvention.

Consequently, the optical fiber fixing members 1 included in the presentinvention are optical fiber fixing members in which peak surfaces arefree surfaces in areas other than those occupied by the free-surfaceportions of edges when at least one of the following edges is a freesurface: edge a, along which the end face 32 located closer to opticalconnections intersects the surface 31 on which optical fiber engagementgrooves 2 are formed, and edge b, along which an end face 33 oppositethe end face 32 located closer to the optical connections intersects thesurface 31 on which the optical fiber engagement grooves 2 are formed.In more specific terms, the following arrangement corresponds to thepresent invention: an arrangement in which the edges are free surfaces,and the peaks are free surfaces in the areas indicated by arrow a in thedirection away from straight line L, which is drawn along the boundarybetween the free surfaces and transfer surfaces of the edges, as shownin FIG. 3. The same applies to line L′.

Another feature of the above-described invention is that the peaksbetween the aforementioned optical fiber engagement grooves shouldpreferably be rounded off in cross section. Peak chipping, damage to theoptical fibers to be fixed, and microcracking can be prevented byrounding off the peaks between the optical fiber engagement grooves inthis manner.

The above-described optical fiber fixing member should preferably becomposed of glass. A member made of a hard material such as glass isvery likely to damage optical fibers. It is therefore possible toachieve higher efficiency in preventing the existence or formation ofmicrocracks.

The optical fiber array of the third invention comprises the opticalfiber fixing member of the above-described invention, optical fiberssecured in the optical fiber engagement grooves of this optical fiberfixing member, and a pressure plate for pressing down said opticalfibers in the optical fiber engagement grooves, the aforementionedoptical fiber fixing member, optical fibers, and pressure plate beingfixedly configured as a unitary structure. Components can be connectedwith better reliability because it is possible to prevent lighttransmission loss from being increased by the microcracking of theoptical fibers.

The method for manufacturing an optical fiber fixing member inaccordance with the fourth invention is a method for manufacturing, bymeans of molding, an optical fiber fixing member having a plurality ofoptical fiber engagement grooves for positioning and fixing opticalfibers, wherein a molding material is pressed by a mold provided withconvexities and concavities corresponding to the aforementioned opticalfiber engagement grooves and the peaks between these optical fiberengagement grooves such that the molding material is forced into theconcavities of the mold; the shape of the convexities of the mold istransferred to the molding material; optical fiber engagement grooveswhose surfaces are mold transfer surfaces are formed; the moldingmaterial is pressure-molded such that the material fills the concavitiesof the mold only partially; a state is maintained in which the shape ofthe bottom portions of the concavities in the mold is not transferred;and peaks are formed between the optical fiber engagement grooves suchthat the surfaces thereof are free surfaces.

Optical fiber fixing members whose peaks have free surfaces and whoseoptical fiber engagement grooves at the same time have mold transfersurfaces can be manufactured with ease merely by performing molding inconditions under which the molding material fills the concavities of themold only partially during molding. In the process, the peaks betweenthe optical fiber engagement grooves are rounded off because the moldingmaterial is forced into the concavities of the mold and the moldingprocess is stopped midway during the rising of the material into theconcavities. It is therefore easy to mold peaks whose surfaces arerounded off and which are prevented from creating microcracks in opticalfibers due to the presence of minute irregularities.

With this method for manufacturing an optical fiber fixing member, it ispreferable that a glass preform be used as the molding material and thatan optical fiber fixing member made of glass be molded in a heatedstate. Optical fiber fixing members that satisfy the fine processingrequirements of submicron precision can be mass-produced at a low costby combining the molding technologies applicable to glass materials withlow coefficients of thermal expansions and to the ultracompact precisionlenses used in optical equipment.

The above-described method for manufacturing an optical fiber fixingmember should preferably be such that the peak surfaces of the portionsdescribed in any of (i) to (iv) below are free surfaces.

(i) Peak surfaces extending all the way in the longitudinal direction ofthe peaks.

(ii) The peak surfaces on the side of the end face located closer tooptical connections (excluding case (i)).

(iii) The peak surfaces on the side of the end face opposite the endface located closer to optical connections (excluding case (i)).

(iv) The peak surfaces on the side of the end face located closer tooptical connections and on the side of the end face opposite the endface located closer to the optical connections (excluding case (i)).

The method for manufacturing an optical fiber array in accordance withthe fifth invention comprises the steps of securing optical fibers inthe grooves of an optical fiber fixing member having a plurality ofoptical fiber engagement grooves for positioning and fixing opticalfibers; pressing the optical fibers in the optical fiber engagementgrooves with a pressure plate; and fixedly configuring the optical fiberfixing member, optical fibers, and pressure plate as a unitarystructure, wherein this method for manufacturing an optical fiber arrayis performed such that a molding material is pressed by a mold providedwith convexities and concavities corresponding to the optical fiberengagement grooves and the peaks between the optical fiber engagementgrooves to force the molding material into the concavities of the mold;the shape of the convexities of the mold is transferred to the moldingmaterial; optical fiber engagement grooves whose surfaces are moldtransfer surfaces are formed; a state is maintained in which the moldingmaterial fills the concavities of the mold only partially; an opticalfiber fixing member is fabricated by forming peaks between the opticalfiber engagement grooves such that, of the surfaces thereof, theportions described in any of (i) to (iii) below are free surfaces; theoptical fibers are sequentially laid out in the grooves in the directionfrom the end face located closer to optical connections toward the endface opposite the end face located closer to the optical connections, insuch a way that the tips of the optical fibers extend sufficiently farbeyond the end face of the optical fiber fixing member located closer tooptical connections, in a state in which the tips of the optical fibersare inclined in relation to the optical fiber engagement grooves; andthe lateral surfaces of the optical fibers are pressed and fixed withthe pressure plate.

(i) Peak surfaces extending all the way in the longitudinal direction ofthe peaks.

(ii) The peak surfaces on the side of the end face located closer tooptical connections (excluding case (i)).

(iii) The peak surfaces on the side of the end face located closer tooptical connections and on the side of the end face opposite the endface located closer to the optical connections (excluding case (i)).

The method for manufacturing an optical fiber array in accordance withthe sixth invention comprises the steps of securing optical fibers inthe grooves of an optical fiber fixing member having a plurality ofoptical fiber engagement grooves for positioning and fixing opticalfibers; pressing the optical fibers in the optical fiber engagementgrooves with a pressure plate; and fixedly configuring the optical fiberfixing member, optical fibers, and pressure plate as a unitarystructure, wherein this method for manufacturing an optical fiber arrayis performed such that a molding material is pressed by a mold providedwith convexities and concavities corresponding to the optical fiberengagement grooves and the peaks between the optical fiber engagementgrooves to force the molding material into the concavities of the mold;the shape of the convexities of the mold is transferred to the moldingmaterial; optical fiber engagement grooves whose surfaces are moldtransfer surfaces are formed; a state is maintained in which the moldingmaterial fills the concavities of the mold only partially; an opticalfiber fixing member is fabricated by forming peaks between the opticalfiber engagement grooves such that, of the surfaces thereof, theportions described in any of (i) to (iii) below are free surfaces; theoptical fibers are sequentially laid out in the grooves in the directionfrom the end face opposite the end face located closer to opticalconnections toward the end face located closer to the opticalconnections, in a state in which the optical fibers are inclined inrelation to the optical fiber engagement grooves, and the tips of theoptical fibers are at a distance from the engagement grooves; and thelateral surfaces of the optical fibers are pressed and fixed with thepressure plate.

(i) Peak surfaces extending all the way in the longitudinal direction ofthe peaks.

(ii) The peak surfaces on the side of the end face opposite the end facelocated closer to optical connections (excluding case (i)).

(iii) The peak surfaces on the side of the end face located closer tooptical connections and on the side of the end face opposite the endface located closer to the optical connections (excluding case (i)).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram depicting a cross section near the optical fiberengagement grooves of an optical fiber fixing member according to anembodiment;

FIG. 2 is a schematic perspective view of an optical fiber fixing memberaccording to an embodiment;

FIG. 3 is a perspective view of an optical fiber fixing member in whichfree surfaces form the edges thereof and extend all the way in thelongitudinal direction of the peaks between V grooves;

FIG. 4 is a schematic perspective view of an optical fiber fixing memberpertaining to an embodiment;

FIG. 5 is a schematic perspective view of an optical fiber arraypertaining to an embodiment;

FIGS. 6 are process drawings illustrating a method for manufacturing anoptical fiber fixing member in accordance with an embodiment with theaid of a mold for manufacturing optical fiber fixing members, where FIG.6a is a front cross-sectional view prior to molding, FIG. 6b is alateral sectional view of the same, FIG. 6c is a front cross-sectionalview during molding, and FIG. 6d is a lateral sectional view of thesame;

FIGS. 7a-7 b are diagrams depicting the manner in which areas in thevicinity of optical fiber engagement grooves are molded with the aid ofa mold having transfer portions for optical fiber engagement grooves inaccordance with the manufacturing method pertaining to an embodiment,where FIG. 7a depicts the initial phase of pressing, FIG. 7b the middlephase, and FIG. 7c the final phase.

FIG. 8 is a perspective view of an optical fiber fixing member in whichfree surfaces form the edges thereof and extend all the way in thelongitudinal direction of the peaks between V grooves;

FIG. 9 is a schematic perspective view of an optical fiber fixing memberin which free surfaces form the tips of the peaks between V grooves andthe intersecting portions of the tip corners;

FIG. 10 is a schematic perspective view of an optical fiber fixingmember in which free surfaces form the back ends of the peaks between Vgrooves and the intersecting portions of the back-end corners;

FIG. 11 is a schematic perspective view of an optical fiber fixingmember in which free surfaces form the front and back ends of the peaksbetween V grooves;

FIG. 12 is a diagram illustrating an example of a method for securingoptical fibers in the optical fiber engagement grooves of an opticalfiber fixing member; and

FIG. 13 is a diagram illustrating the conditions for providing the peakswith free surfaces.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described.

The optical fiber fixing member of the present invention is a glassmember provided with eight optical fiber engagement grooves and designedto form an eight-core optical fiber array for aligning and fixing eightoptical fibers. The member is shaped as a block having a step 3, asshown in FIG. 4. The member is designed such that the pitch between theoptical fibers is 250 μm when these optical fibers (diameter: 125 μm)are laid out and secured in the optical fiber engagement grooves 2. FIG.1 is a cross section of the optical fiber fixing member 1 in thevicinity of the optical fiber engagement grooves 2. The cross section isperpendicular to the optical axes of optical fibers F secured in theoptical fiber engagement grooves 2. The optical fiber engagement grooves2 have generally V-shaped cross sections, and the opening angle of theV-shape is 70°. Peaks 5 for separating the engagement grooves from eachother are formed between the optical fiber engagement grooves 2.

Whereas the surfaces of the optical fiber engagement grooves 2 (whichsupport the lateral surfaces f of the optical fibers F when these fibersare secured) are mold transfer surfaces 6 transferred from the mold, thesurfaces of the peaks 5, which are positioned between the engagementgrooves 2, are composed of free surfaces 7 not in contact with the mold,and the cross sections thereof are generally circular arcs having acertain degree of roundness. The width of the free surfaces 7 in theaforementioned cross sections should preferably be 10-80 μm, and theradius of curvature of the aforementioned circular arcs should be 25-50μm. It is particularly preferable for both the width and the radius ofcurvature to fall within the aforementioned ranges. When the width ofthe free surfaces is less than 10 μm, the release properties of themolding are adversely affected, and molding burrs tends to form. Whenthe width exceeds 80 μm, free shrinkage of glass increases, and moldingaccuracy decreases. When the radius of curvature is less than 25 μm, awider surface area is occupied by minute irregularities, making it morelikely that the lateral surfaces of fibers will be damaged when thefibers are arranged and fixed in place. When the radius exceeds 50 μm,the fibers extend further beyond the top of the peaks between the Vgrooves, adversely affecting durability or the polishing characteristicsof end faces.

A material with a low yield point and a low coefficient of thermalexpansion suited to precision molding may be used as the glass materialfor the optical fiber fixing member. A material with high UVtransmissivity is preferred because of the use of a UV-curing adhesive.

Single-mode fibers F made of quartz glass were aligned in the opticalfiber engagement grooves 2 of such an optical fiber fixing member,pressed down with a pressure plate 10, and fixed in place with aUV-curing adhesive 12 while exposed to UV light. The pressure plate 10and the end face of the optical fiber fixing member 1 facing the opticalconnections were polished at the same time together with the end facesof the optical fibers thus fixed, yielding an eight-core optical fiberarray 11 such as that shown in FIG. 5. Pairs of optical fiber arrays 11thus obtained were abutted with each other along their end faces andfixed in place after the optical axes of the corresponding pairs ofoptical fibers F were aligned. Light was then passed through the otherend of an optical fiber, and this light was transmitted into a connectedoptical fiber. Transmission loss was measured, but no increase intransmission loss due to microcracking was observed. The ambienttemperature was then varied between −40 and +85° C. over a course ofabout 1000 cycles, but no increase in transmission loss or optical fiberbreakage was observed at all.

Such an optical fiber array was disassembled, and the lateral surfacesfixed in the optical fiber engagement grooves for optical fibers wereexamined under an optical or electron microscope. It was found that nomicrocracks had formed as a result of alignment and fixing. When anoptical fiber fixing member is composed of glass (as in the case of thisembodiment), this material is harder than a material such as resin orthe like, making it highly likely that the lateral surfaces of theoptical fibers will be damaged by the minute irregularities. The presentinvention is therefore capable of demonstrating a more remarkable effectwith respect to glass products than when these products are composed ofa material (such as resin) softer than that used for optical fibers.

Following is a description of a method for manufacturing the opticalfiber fixing member of the present embodiment with the aid of a mold.

As shown in FIG. 6, an upper die 21 for forming surfaces that containthe optical fiber engagement grooves of the optical fiber fixing member,a lower die 42 that faces the upper die 21, and a frame die 43 forforming the lateral surfaces of the optical fiber fixing member areassembled together; and a glass preform G located in a cavity 44 definedby the molding dies 21, 42, and 43 is molded in a heated state. Themolding surfaces of the molding dies 21, 42, and 43 are covered withrelease films. The glass preform G is placed in the cavity 44 of themold, pressure is applied while the mold is heated, and the glasspreform G is molded under molding conditions in which the shape of thepeaks of the molded article falls within a range suited to freesurfaces. Molding is followed by cooling to room temperature and aconcurrent pressure reduction, and the molded article 45 is then takenout of the mold. It is also possible to use a die 21 as the lower die,to use a die 42 as the upper die, and to perform molding by placing theglass preform G on the molding surface of the lower die 21 formed into aunitary structure with the frame die 43.

FIG. 7 is a cross section of the portion molded by transferring theoptical fiber engagement grooves of the upper die 21. This is a moldcross section that corresponds to the cross section of an optical fiberfixing member shown in FIG. 1 and that depicts the manner in which theglass preform G fills the concavities 25 serving as the transferportions 20 of the optical fiber engagement grooves during pressing. Thetransfer portions 20 of the optical fiber engagement grooves consist ofconcavities 25 and convexities 26. Although the concavities 25 of themold 21 describe acute angles in FIG. 7, the actual cross section of abottom portion 25 a has a shape resembling that of a circular arc with aradius of curvature of no more than 20 μm. The concavities 25 betweenthe convexities 26 of the mold 21 are formed by grinding, and minuteirregularities are observed to have formed on the transfer surfaces(ground surfaces) 27.

In the present embodiment, however, optical fiber engagement portionshaving at least engagement grooves 2 and peaks 5 are formed while theglass preform G fills the aforementioned concavities 25 only partiallyby selecting molding conditions in an appropriate manner, and molding isperformed such that the surfaces that support the lateral surfaces f ofthe optical fibers are mold transfer surfaces 6.

Specifically, the glass preform G is pressed by the mold 21 such thatthe glass preform G fills the concavities 25 of the mold 21 providedwith the convexities 26 and concavities 25 for transferring the peaks 5located between the optical fiber engagement grooves 2. In the pressingstep, the shape of the convexities 26 of the mold 21 is transferred tothe glass preform G, forming optical fiber engagement grooves 2 andmaking their surfaces mold transfer surfaces 6. Pressure forming isperformed under molding conditions (temperature, pressure, molding time,ratio of mold capacity and preform volume, and the like) in which theglass preform G fills the concavities 25 of the mold 21 only partially,a state is maintained in which the shape of the bottom portions 25 a ofthe concavities 25 in the mold 21 is not transferred, and peaks 5 areformed between the optical fiber engagement grooves 2 such that thesurfaces thereof are free surfaces 7. The minute irregularities of themold 21 are not transferred because the free surfaces 7 of the peaks 5between the optical fiber engagement grooves 2 thus molded are not incontact with the mold 21. In addition, the radius of curvature of thepeaks 5 of the molded article is always greater than the radius ofcurvature of the concavities 25 of the mold 21.

The molded article is taken out of the mold 21 following molding, butbecause the glass preform G fills the concavities 25 of the mold 21 onlypartially, the molded article can be taken out of the mold 21 using lessforce than in the case of conventional molding.

Another feature is that when the glass preform G is molded such thatfree surfaces 7 are formed between adjacent optical fiber engagementgrooves 2, the glass preform G fills the concavities 25 of the opticalfiber engagement groove transfer portions 20 of the mold 21 onlypartially, preventing the mold 21 and the molded article from adheringto each other near the optical fiber engagement grooves 2. The releaseproperties of the molded article are therefore improved during theremoval of the molded article from the mold 21 following molding.

Yet another feature is that when the fill factor of the glass preform Gin relation to the volume of the cavity in the mold 21 is kept low (asin the molding process described above), the offset of the preformposition in relation to the mold 21 increases, as does the surplus moldcapacity for absorbing excess preform G, making it less likely that theglass preform G will penetrate into the gaps of the mold 21, andbroadening the range of burr-less molding conditions (conditions underwhich molding can be conducted without the accompanying burring). It isalso possible to broaden the range of molding conditions under whichconstant results are obtained for the accuracy of the transfer surfaces27 of the optical fiber engagement groove transfer portions 20 accordingto the requirements of high-accuracy transfer molding, and for theaccuracy of the intervals between the optical fiber engagement grooves2. This is because the free surface or the strain-absorbing excess moldcapacity increases when the molded article and the mold 21 undergocontraction in the cooling step of the molding process.

Breakage of the molded article can thus be prevented due to improvementsin release properties and burr control properties. In addition, havingfree surfaces 7 is preferred from the standpoint of preventing releasefilms from peeling off from the mold 21 during repeated molding.

Another feature is that because the glass preform G fills theconcavities 25 of the optical fiber engagement groove transfer portions20 of the mold 21 only partially, the surfaces of the concave bottomportions 25 a do not function as mold transfer surfaces, and the formaccuracy of the peaks 5 between the optical fiber engagement grooves 2of the molded article does not depend any longer on the form accuracy ofthe concave bottom portions 25 a of the mold. It is therefore possibleto increase the tolerance of the form accuracy of the concave bottomportions 25 a of the mold (particularly the tolerance of the radius ofcurvature of the concave bottom portions 25 a, as viewed in a crosssection perpendicular to the drawing direction of the concavities 25),facilitating the grinding of available molds 21. Because a mold can befabricated by less complicated machining, a method for manufacturingoptical fiber fixing members with high productivity can be providedconjointly with the above-described effect of preventing the peeling ofrelease films, the effect of preventing breakage of molded articles, andthe like. The preform of the present invention is not limited to glass.For example, plastics may also be used, provided they can be molded withhigh accuracy.

Another feature of this embodiment is that peaks are allowed to shrinkfreely during cooling and that shrinkage strain (stress) can be reducedduring the molding of the entire molded portion of optical fiberengagement grooves by performing the molding process such that the peaksbetween the optical fiber engagement grooves remain free surfaces. As aresult, it is possible to reduce the cracking and other types of damageoccurring during thermal shock tests or the like in areas adjacent tothe optical fiber engagement grooves, and particularly in the bottomportions, where stress is apt to concentrate because of structuralfactors.

In addition, the edges a and b (portions where surfaces intersect eachother) of the optical fiber fixing member can be formed by free surfacesbecause molding is performed such that the peaks between the opticalfiber engagement grooves are free surfaces (FIG. 2). Burring along theedges of the optical fiber fixing member can be prevented by makingthese edges into free surfaces. Release properties can be furtherimproved, and damage to the molded article, the mold, and the releasefilms during the release step can be reduced by performing molding insuch a way that edges (in addition to peaks) are composed of freesurfaces.

A study was subsequently conducted into the effects of formingfree-surface portions at various locations in the longitudinal directionof peaks.

The optical fiber fixing member of the present invention includes thefollowing aspects.

(1) Free surfaces constitute peak surfaces all the way in thelongitudinal direction of peaks 5 (symbol A in FIG. 8).

(2) Free surfaces are limited to the portions of the peaks lying alongthat end face 32 of an optical fiber fixing member 1 which is locatedcloser to optical connections, that is, along the end face through whichlight enters optical fibers when these optical fibers are disposed inoptical fiber engagement grooves 2 (symbol B in FIG. 9).

(3) Free surfaces are limited to the portions of peaks 5 facing an endface 33 opposite the end face 32 located closer to optical connections(symbol C in FIG. 10).

(4) Free surfaces are limited to the portions of peaks 5 that face theend face 32 located closer to optical connections and that face the endface 33 opposite the end face 32 located closer to the opticalconnections (symbols B and C in FIG. 11).

In each aspect, release is easier to achieve than when the peak portionsalong the end face located closer to optical connections and the peakportions along the end face opposite the end face located closer tooptical connections are not free surfaces, and only the middle portionsof the peaks are free surfaces. Another feature of these aspects is thatthe formation of burrs in areas where the optical fiber engagementgrooves come into contact with the edges of the molded article can beprevented because the peak portions near the edges are free surfaces.

The above-described aspects (1)-(4) of free surfaces are alsoadvantageous when an optical fiber array is fabricated using theabove-described optical fiber fixing member. A description follows. Thefollowing two methods may be used to prevent the end faces of opticalfibers from being damaged when these optical fibers are laid out andsecured in optical fiber engagement grooves.

(A) According to the first method, optical fibers are sequentially laidout and secured in the optical fiber engagement grooves in such a waythat the tips of the optical fibers extend sufficiently far beyond theend face located closer to optical connections and that the opticalfibers are held at an incline and are placed into the optical fiberengagement grooves from the side of the end face located closer to theoptical connections.

Specifically, as shown in FIG. 12, an optical fiber F is inclined inrelation to an optical fiber engagement groove 2, an optical fiberstrand 42 is first inserted into the optical fiber engagement groove 2from the side of the end face 32 located closer to optical connectionswhile the tip 43 of the optical fiber is extended beyond the end face 32located closer to the optical connections, and the optical fiber strand42 is then gradually introduced into the engagement groove 2. Theoptical fiber strand 42 is gradually slid along the optical fiberengagement groove 2 toward the end face 32 located closer to the opticalconnections until the end near the tip portion of the cladding 41 of theoptical fiber presses against, or moves close to, the end face 33opposite the end face 32 located closer to the optical connections. Thelateral surfaces of the optical fiber are then pressed and fixed inplace with a pressure plate, yielding an optical fiber array.

(B) According to the second method, an optical fiber is gradually laidout and fixed in an optical fiber engagement groove in such a way thatthis optical fiber is placed into the groove in the direction from theportion of the optical fiber engagement groove facing the end faceopposite the end face located closer to optical connections (in thedirection toward the end face located closer to the optical connections)while the tip of the optical fiber is kept at a distance from theoptical fiber engagement groove. In this method, the optical fiberstrand 42 is gradually inserted into the engagement groove 2 in thedirection opposite that in FIG. 12, that is, from the end face 33opposite the end face 32 located closer to the optical connectionstoward the end face 32 located closer to the optical connections.

In (A) above, the lateral surfaces of optical fibers are first broughtinto contact with the end faces of the optical fiber engagement grooveslocated closer to optical connections. Irrespective of the aspectassumed by the above-described free surfaces (1), (2), or (4) in theoptical fiber fixing member used in this case, the lateral surfaces ofthe optical fibers can be easily accommodated by the optical fiberengagement grooves because the portions of the peaks in the vicinity ofthe optical fiber engagement grooves that first come into contact withthe lateral surfaces of the optical fibers are free surfaces. Inaddition, microcracking or another type of damage is less likely tooccur when the lateral surfaces of the optical fibers come into contactwith the peaks between the optical fiber engagement grooves becausethese peaks are free surfaces.

In (B) above, the lateral surfaces of the optical fibers are firstbrought into contact with those end faces of the optical fiberengagement grooves which are opposite the end faces located closer tooptical connections. The portions of the peaks located in the area wherethe optical fibers are first inserted should preferably be freesurfaces. It is even more preferable for the edges of the optical fiberfixing member in the area of initial contact with the optical fibers tobe composed of free surfaces. Irrespective of the aspect assumed by thefree surfaces (1), (3), or (4) in the optical fiber fixing member usedin this case, the lateral surfaces of the optical fibers can be easilyaccommodated by the optical fiber engagement grooves because theportions of the peaks in the vicinity of the optical fiber engagementgrooves that first come into contact with the lateral surfaces of theoptical fibers are free surfaces. In addition, microcracking or anothertype of damage is less likely to occur when the lateral surfaces of theoptical fibers come into contact with the peaks between the opticalfiber engagement grooves because these peaks are free surfaces.

Aspects (1)-(4) above are therefore preferred. In the particular case ofaspects (2)-(4), peak sections composed of transfer surfaces and peaksections composed of free surfaces are distributed in the longitudinaldirection of the peaks, and the radius of curvature Of the peaks changescontinuously in the longitudinal direction of the peaks. Optical fiberscan therefore be laid out smoothly when they are arranged and secured inoptical fiber engagement grooves by a method such as A or B above. Inaddition, the radius of curvature of the peaks is reduced at least nearthe locations at which optical fibers are first placed in the groovesduring their gradual placement, providing an arrangement that canprevent an optical fiber already received by an optical fiber engagementgroove from slipping out of the optical fiber engagement groove whenmethod A or B is carried out.

Furthermore, the molding material is deformed to a large extent andresidual strain is likely to form near the edges of a molded articleobtained by molding, so adopting free surfaces for the peaks in theareas near the edges as in aspects (1)-(4) above is preferred from thestandpoint of achieving stress relaxation near the optical fiberengagement grooves and reducing the damage to the optical fiber fixingmember. Adopting free surfaces for the edges in contact with opticalfiber engagement grooves is particularly preferred for reducing thedamage to the optical fiber fixing member because of a more pronouncedstress relaxation effect.

As noted above, mold temperature, molding pressure, and molding time aresome of the conditions that allow peaks to be provided with freesurfaces, that is, some of the parameters that control the formation ofthe free surfaces. FIG. 13 is a diagram illustrating the shapeattributes (peak, edge, angular portion) of a molded articlecorresponding to various parameters. The glass used in this casecontains the following glass components: 3-30 wt % SiO₂, 20-40 wt %B₂O₃, 40-55 wt % ZnO (excluding 40 wt %), 0-15 wt % MgO, 0-10 wt % CaO,0-10 wt % SrO, 0-10 wt % BaO, 0-20 wt % PbO, 40-55 wt %ZnO+MgO+CaO+SrO+BaO+PbO (excluding 40 wt %), 0.5-10 wt % Al₂O₃, and 0-7wt % Li₂O. The content of the aforementioned glass components is 75 wt %or higher. The glass that can be used in the present invention is notlimited to the one described above, however. These conditions changewith the use of a different molding apparatus or the like, and must thusbe customized for the particular apparatus.

INDUSTRIAL APPLICABILITY

With the optical fiber fixing member and optical fiber array of thepresent invention, microcracks can be prevented from forming on thelateral surfaces of optical fibers secured in the optical fiberengagement grooves of the optical fiber fixing member, so thetransmission loss of light transmitted by the optical fibers can beprevented from decreasing.

In addition, the method for manufacturing optical fiber fixing membersand the method for manufacturing optical fiber arrays in accordance withthe present invention allow optical fiber fixing members whose peakshave free surfaces and whose optical fiber engagement grooves at thesame time have mold transfer surfaces to be manufactured with easemerely by selecting the appropriate molding conditions during molding.

What is claimed is:
 1. A method for manufacturing, by means of molding,an optical fiber fixing member having a plurality of optical fiberengagement grooves for positioning and fixing optical fibers, whereinsaid method for manufacturing an optical fiber fixing member ischaracterized in that a preform is pressed by a mold provided withconvexities and concavities corresponding to said optical fiberengagement grooves and the peaks between the optical fiber engagementgrooves such that the preform is forced into the concavities of saidmold, the shape of the convexities of said mold is transferred to thepreform, and optical fiber engagement grooves whose surfaces are moldtransfer surfaces are formed; and the molding material ispressure-molded such that the material fills the concavities of saidmold only partially, a state is maintained in which the shape of thebottom portions of the concavities in said mold is not transferred, andpeaks are formed between the optical fiber engagement grooves such thatthe surfaces thereof are free surfaces.
 2. The method for manufacturingan optical fiber fixing member according to claim 1, characterized inthat a glass preform is used as the molding material, and an opticalfiber fixing member made of glass is molded in a heated state.
 3. Themethod for manufacturing an optical fiber fixing member according toclaim 2, characterized in that the peak surfaces of the portionsdescribed in any of (i) to (iv) below are free surfaces: (i) Peaksurfaces extending all the way in the longitudinal direction of thepeaks; (ii) The peak surfaces on the side of the end face located closerto optical connections (excluding case (i)); (iii) The peak surfaces onthe side of the end face opposite the end face located closer to opticalconnections (excluding case (i)); (iv) The peak surfaces on the side ofthe end face located closer to optical connections and on the side ofthe end face opposite the end face located closer to the opticalconnections (excluding case (i)).
 4. A method for manufacturing anoptical fiber array, comprising the steps of: securing optical fibers inthe grooves of an optical fiber fixing member having a plurality ofoptical fiber engagement grooves for positioning and fixing the opticalfibers; pressing said optical fibers in said optical fiber engagementgrooves with a pressure plate; and fixedly configuring said opticalfiber fixing member, optical fibers, and pressure plate as a unitarystructure, wherein said method for manufacturing an optical fiber arrayis characterized in that a molding material is pressed by a moldprovided with convexities and concavities corresponding to said opticalfiber engagement grooves and the peaks between the optical fiberengagement grooves such that the molding material is forced into theconcavities of said mold, the shape of the convexities of said mold istransferred to the molding material, optical fiber engagement grooveswhose surfaces are mold transfer surfaces are formed, a state ismaintained in which the molding material fills the concavities of saidmold only partially, and an optical fiber fixing member is fabricated byforming peaks between the optical fiber engagement grooves such that, ofthe surfaces thereof, the portions described in any of (i) to (iii)below are free surfaces; said optical fibers are sequentially laid outin said optical fiber engagement grooves, starting from the side of theend face located closer to optical connections, in such a way that thetips of the optical fibers extend sufficiently far beyond the end faceof said optical fiber fixing member located closer to opticalconnections, in a state in which the tips of the optical fibers areinclined in relation to said grooves; and the lateral surfaces of saidoptical fibers are pressed and fixed with said pressure plate; (i) Peaksurfaces extending all the way in the longitudinal direction of thepeaks; (ii) The peak surfaces on the side of the end face located closerto optical connections (excluding case (i)); (iii) The peak surfaces onthe side of the end face located closer to optical connections and onthe side of the end face opposite the end face located closer to theoptical connections (excluding case (i)).
 5. A method for manufacturingan optical fiber array, comprising the steps of: securing optical fibersin the grooves of an optical fiber fixing member having a plurality ofoptical fiber engagement grooves for positioning and fixing opticalfibers; pressing said optical fibers in said optical fiber engagementgrooves with a pressure plate; and fixedly configuring said opticalfiber fixing member, optical fibers, and pressure plate as a unitarystructure, wherein said method for manufacturing an optical fiber arrayis characterized in that a molding material is pressed by a moldprovided with convexities and concavities corresponding to said opticalfiber engagement grooves and the peaks between the optical fiberengagement grooves such that the molding material is forced into theconcavities of said mold, the shape of the convexities of said mold istransferred to the molding material, optical fiber engagement grooveswhose surfaces are mold transfer surfaces are formed, a state ismaintained in which the molding material fills the concavities of saidmold only partially, and an optical fiber fixing member is fabricated byforming peaks between the optical fiber engagement grooves such that, ofthe surfaces thereof, the portions described in any of (i) to (iii)below are free surfaces; said optical fibers are sequentially laid outin said grooves in the direction from the end face opposite the end facelocated closer to optical connections toward the end face located closerto the optical connections, in a state in which said optical fibers areinclined in relation to said optical fiber engagement grooves, and thetips of the optical fibers are at a distance from said grooves; and thelateral surfaces of said optical fibers are pressed and fixed with saidpressure plate; (i) Peak surfaces extending all the way in thelongitudinal direction of the peaks; (ii) The peak surfaces on the sideof the end face opposite the end face located closer to opticalconnections (excluding case (i)); (iii) The peak surfaces on the side ofthe end face located closer to optical connections and on the side ofthe end face opposite the end face located closer to the opticalconnections (excluding case (i)).